Fermentation processes are used for making a vast number of commercial products, including alcohols (e.g. ethanol, methanol, butanol, 1,3-propanediol); organic acids (e.g., citric acid, acetic acid, itaconic acid, gluconic acid, gluconate, lactic acid, succinic acid, 2,5-diketo-D-gluconic acid; ketones (e.g., acetone); amino acids (e.g. glutamic acid); gases (e.g., H2 and CO2), and more complex compounds, including, for example, antibiotics (e.g., penicillin and tetracycline); enzymes; vitamins (e.g., riboflavin, B12, beta-carotene); hormones, and other compounds which are difficult to produce synthetically. Fermentation processes are also commonly used in dairy (e.g., in the production of yogurt and cheese), leather, and tobacco industries.
Fermentation products are produced industrially in large fermentation tanks capable of holding upwards of 10 cubic meters fermentation medium. In order to build up a suitable fermenting organism population and concentration in the fermentation tank a fermentation process usually requires a process time of between 48 and 120 hours or more. Because of the large-sized tanks and long fermentation times it is difficult to maintain the fermentation system free of contamination. Unwanted contaminant bacteria are often gram-positive bacteria from the genus Lactobacillus that converts glucose into lactic acid and acetic acid. Also gram-negative bacteria are known to contaminate fermentation processes. Unfortunately the fermentation conditions are usually conducive for bacterial growth. If bacterial contamination occurs the entire fermentation tank must be emptied, cleaned and sterilized and the fermentation medium is useless. This is of course time-consuming and costly. Further, many bacteria compete with the fermenting organism for the sugar. This results in a reduced fermentation yield.
Bayrock et al., 2003, Appln. Microbiol. Biotechnol. 62:498-502 disclose control of Lactobacillus contaminants in continuous fuel ethanol fermentations by constant or pulse addition of penicillin G.
Today antibiotics, heat and chemical disinfectants are used for killing and/or inhibiting growth of unwanted bacteria. These disinfectants are added to the fermentation before or during fermentation, The known antibacterial agents including antibiotics, such as penicillin, are sometimes not desired. Therefore, there is a need for further means for killing and/or inhibiting unwanted bacteria growth during fermentation processes.